The present invention relates to a method for a valve, a valve and a wire line core drilling system including such a valve.
It is known in various connections to use valves that control the supply of a fluid by being opened when they are subjected to a certain pressure from the fluid. One such application is in wire line core drilling, as will be described below.
When performing exploratory drilling to collect rock samples from depths of from several hundred to a couple of thousand meters, double core tubes are used having an inner and an outer tube. The sample is collected in the inner tube, which usually has a length of a few meters. When the inner tube is full this is usually detected by means of a manometer or the like that measures the flushing water pressure in the core tube. A retriever device suspended on a wire is lowered into the tube for retracting the inner tube with the sample, said retriever device comprising a gripping means in the form of a claw or xe2x80x9cspearheadxe2x80x9d arranged to engage with a gripping means arranged on/in the upper end of the inner tube. When the wire is then tautened the inner tube is disengaged from the outer tube, and the inner tube with the sample can be hoisted up. Conversely, the claw and the gripping means on the inner tube can be used to lower a new inner tube. Equipment of this type is generally known as a wire line system.
When a new inner tube is inserted it is important to be able to ascertain that the inner tube really has reached right down to the bottom of the outer tube and has assumed its correct position for drilling, before drilling is commenced. Ascertainment that the tube can no longer move, but is firmly held is generally taken as an indication that the inner tube has reached its correct position. According to known technology, therefore, the gripping means is often designed to be combined with some type of locking member that firmly locks the inner tube in relation to the outer tube when the inner tube has reached the correct position. This locking member usually consists of a hook-like device, preferably spring-loaded, a locking claw or latch that engages with recesses or shoulders arranged in the inside of the outer tube. Actual insertion of the inner tube is usually performed by the inner tube being xe2x80x9cpumpedxe2x80x9d along inside the drill string with the aid of water. When the inner tube is firmly in place the water pressure will increase to such an extent that a valve arranged for flushing medium in the inner tube is released.
One problem with such known arrangements is that when the inner tube is inserted into the drill string it sometimes catches before it has reached the correct position for drilling. With designs currently in use, the increase in water pressure then occurring will release the flushing valve before the inner tube has reached its correct position and, in the worst case, drilling will be commenced. This primarily entails a disadvantage from the financial point of view since the drilling will be into thin air. There is also a risk of the core at the bottom being destroyed.
The primary object of the present invention is to remedy the problems described above.
The object of the invention is achieved by means of a method as defined in claim 1, a valve as defined in claim 5, and a wire line core drilling system as defined in claim 9.
In accordance with the present invention, therefore, a method is defined for a valve, which valve comprises a movable valve body having a first side facing a means for supplying pressurised fluid and influenced in the supply direction by a force from said fluid, and a second side influenced in opposite direction by a force from said fluid, which valve is provided with at least one connection connecting the first side of the valve body with the second side of the valve body, and also comprising a spring for opening the valve by displacing the valve body from a closed position to an open position, said method comprising the following steps:
a pressurised fluid is supplied to the valve in closed position whereupon the valve remains closed,
the supply of pressurised fluid to the closed valve ceases,
a force equalisation then occurs between said first and second sides in that fluid flows through the connection, thereby enabling the spring to open the valve, and
a pressurised fluid is supplied to the valve in open position and the valve remains open.
The present invention thus offers the advantage that the valve is not opened immediately an increase in pressure is obtained, but opening is delayed. This is particularly advantageous, for instance, when the valve is being used in conjunction with a wire line core drill.
The valve is advantageously provided with a locking device to mechanically lock the valve when it is in closed position, and the method then comprises the following favourable features:
the pressurised fluid is supplied to the valve in closed and mechanically locked position,
the locking device is caused to cease locking said valve in closed position,
the valve continues to be closed even when the locking device no longer locks the valve, since the pressurised fluid supplied still causes the valve to remain closed,
the supply of pressurised fluid ceases, and
a force equalisation then occurs between said first and second sides, thereby enabling the spring to open the valve.
The features defined above offer the advantage of double security, since the valve not only has delay function, but is also mechanically locked in closed position.
The method is performed using a valve as defined in claim 5.
In accordance with the particularly advantageous application of the invention in wire line core drilling, the advantages are obtained that the flush valve is not released until the inner tube has assumed the correct position inside the outer tube for drilling and that when the valve is released, this occurs mechanically with the aid of the locking device in accordance with the invention. It is thus not released as a result of an increase in pressure, and the risks associated with previously known pressure-released arrangements are therefore eliminated. There is therefore no risk of drilling being commenced before the inner tube is safely in place. The completion of all steps in the method may also be used with advantage as an indication that the inner tube has assumed the correct position in the outer tube and that drilling may be commenced. For this purpose a signal may be conveyed to a drill rig. This is particularly advantageous with modern, computer-controlled drill rigs. A system for wire line core drilling provided with a valve in accordance with the invention, thus advantageously includes means for transmitting a signal to a drill rig, which signal indicates that the inner tube has assumed the correct position inside the outer tube, that the valve has been opened and that drilling can be commenced.
Additional features and advantages are revealed in the subordinate claims.